This application claims the priority of Korean Patent Application No. 2002-81864 filed Dec. 20, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a method and apparatus for performing compression bonding, and more particularly, to a method and apparatus for performing compression bonding on an optical element, which is formed of silica glass having a transparency with respect to UV light, with an aluminum layer formed on a substrate.
2. Description of the Related Art
An increase in attention paid to optical communication systems has triggered the development of optical communication devices that are widely used in communication networks. In general, an optical communication device is fabricated by disposing a plurality of optical elements, such as a lens, a prism, and an optical fiber, all of which are formed of silica glass, on a silicon substrate.
To fabricate optical communication devices, a bonding process of bonding such optical elements to a predetermined position of the silicon substrate is required. An organic adhesive is used to bond such optical elements to the silicon substrate, but the organic adhesive pollutes the optical elements and electronic circuits. Thus, it is preferable that optical elements are bonded to a substrate without an adhesive in optoelectronic packaging fields.
FIG. 1 is a cross sectional view illustrating the compression bonding method disclosed in U.S. Pat. No. 5,178,319, which is an example of a conventional compression bonding method. Referring to FIG. 1, a surface of a silicon substrate 12 is coated with an aluminum layer 13, a surface of which is bonded to a spherical glass lens 11. The glass lens 11 is compressed on the aluminum layer 13 in the direction of an arrow 15, using a bonding apparatus 14, and simultaneously, the aluminum layer 13 is heated by a heater 16.
As described above, in the conventional compression bonding method, the glass lens 11 is bonded to the aluminum layer 13 coated on the silicon substrate 12 by heating the aluminum layer 13 while applying a pressure on the glass lens 11. Great care must be paid when applying heat and pressure on the spherical glass lens 11, so that the glass lens 11 is firmly attached to the aluminum layer 13 but not severely deformed or damaged. More specifically, heat and pressure are applied on the glass lens 11 within a range where the glass lens 11 is not softened or deformed. The applied pressure causes a curved surface of the spherical glass lens 11 to rupture an aluminum oxide film, which is natively formed on the aluminum layer 13, thereby having it so the silicon glass lens 11 directly contacts the pure aluminum of the aluminum layer 13.
The conventional compression bonding method is based on conditions where the optical elements, which are disposed on an optical platform, are of smaller sizes and a contact area between the optical elements and an aluminum layer is narrow. Therefore, when pressure is applied onto the optical elements within a range where the optical elements are not severely deformed, the optical elements can be penetrated into the aluminum layer. However, with the conventional compression bonding method, it is difficult to generate a sufficient bonding strength between the optical elements and the aluminum layer. The bonding mechanism of the conventional compression bonding method can be explained by a chemical-mechanical hypothesis. In particular, a chemical interaction between silica, which is a material used for a glass lens, and aluminum coated on a substrate is one major means to strengthen the bonding of the optical elements with the aluminum layer. However, silica does not substantially react with aluminum at room temperature. Thus, a bonding process temperature must be increased to 320° C., for example, in order to accelerate the chemical interaction of silica with aluminum when performing the conventional compression bonding method. However, 320° C. is high and designing a packaging process for an optical communication device in that temperature may cause critical thermal stress and failure of the optical communication device.